Project Summary The goal of this work is to characterize changes in visual processes that transform the 2-dimensional retinal image into object-based 3-dimensional representations of the world as a function of location within the visual field. These processes?referred to collectively as perceptual organization?are critical to the success of more complex visual tasks including important everyday tasks like reading, recognizing individuals, and following dynamic events on a screen or in the world. The underlying neurophysiology of the most fundamental components of perceptual organization suggest the hypothesis that perceptual organization is relatively poor for information in peripheral regions of the visual field compared to central regions. We will test that hypothesis in this work. Part of the significance of this work is that macular degeneration, which is the leading cause of blindness in people over the age of 65, and is expected to affect nearly 2 million individuals in the U.S. by 2020, is characterized by progressive loss of vision in central regions of the visual field. Individuals with macular degeneration therefore have to learn to rely on information in their periphery, and many interventions for the disease focus on increasing the size of peripheral information to compensate for known decreases in spatial resolution with eccentricity. Despite the success of these interventions to improve sensitivity to peripheral stimuli, many patients continue to suffer dysfunction in more complex, and critical for everyday life, tasks such as reading and recognizing faces. We hypothesize that an important part of this residual dysfunction is caused by the need to rely on peripheral perceptual organization which yields relatively poor 3D models of the world, even if edges and other low-level features are perfectly discriminable. This project will (1) quantify a set of four basic perceptual organization processes that are directly relatable to the simple neurophysiological mechanisms that have been identified and that provide motivation for the basic hypothesis, (2) test the hypothesis that an important downstream process that depends on perceptual organization ? object-based attention ? also decreases in effectiveness in more peripheral regions of the visual field and (3) test the hypothesis that changes in perceptual organization as a function of location in the visual field can predict changes in object-based attention within individual observers. If this work provides support for the basic hypotheses being tested, then follow-up work will extend the measurements to patients with central visual-field loss and ask whether their specific dysfunctions can be accounted for by reliance on relatively poor perceptual organization and if so, seek to develop interventions that either improve or compensate specifically for this dependence.